I'm definitely not arguing that there isn't something unusual about him. But your statement that one or both his parents cannot be his actual parents is an assumption, not something established by evidence. Same with the supposition that the Templars wanted to keep him under control.The attitudes of several creatures and organizations around him seem to suggest he is beyond trivial. He is treated as an important asset and put under vigilance by others who are not his parents and would have no reason for that. He could be an experiment, he could be a child from supernatural beings or at least half human. His storyline and future character development is implied to involve nordic deities and other beings that would not give further attention to a tiny mortal. I think that in the next chapter he will deal with powers and beings beyond human grasp. His true nature, and his potential brought attention upon him from people, beings and organizations. The templars wanted to keep him under their control.
Are these things possible? Sure. But until there's more evidence available we cannot objectively conclude that they are true.